This invention relates generally to hydrocarbon conversion catalyst regeneration that employs a halogen-containing compound.
Although catalysts for the conversion of hydrocarbons have a tendency to deactivate, usually a catalyst""s activity may be restored by one of a number of processes that are known generally as regeneration processes. Regeneration processes are extensively used. What specific steps comprise a regeneration process depend in part on the reason for the deactivation. For example, if the catalyst deactivated because coke deposits accumulated on the catalyst, regeneration usually includes removing the coke by burning. If the catalyst deactivated because a catalytic metal such as platinum became agglomerated, regeneration usually includes redispersing the metal by contacting the catalyst with oxygen and chlorine. If the catalyst deactivated because a catalytic promoter such as chloride became depleted, regeneration usually includes replenishing the promoter by contacting the catalyst with a chlorine-containing species. Operating conditions and methods for these regeneration processes are well known. Regeneration processes can be carried out in situ, or the catalyst may be withdrawn from the vessel in which the hydrocarbon conversion takes place and transported to a separates regeneration zone for reactivation. Arrangements for continuously or semicontinuously withdrawing catalyst particles from a reaction zone and for reactivation in a regeneration zone are well known.
Many of these regeneration processes share the common feature of introducing one or more chlorine-containing compounds into the regeneration zone in order to restore the activity of the catalyst for use in the reaction zone. Although chlorine is sometimes introduced into the regeneration zone, it is much more common that one of several chlorine-containing compounds, such as 1,1 dichloroethane, 1,2 dichloroethane, 1,1 dichloropropane, and 1,2 dichloropropane, is introduced into the regeneration zone. The most commonly used compounds thus contain not only chlorine but also carbon and/or hydrogen. Many regeneration zones into which these compounds are introduced typically contain molecular oxygen and operate at conditions that have been carefully optimized with a view towards combusting coke deposits on the catalyst or towards oxidizing or dispersing a catalytic metal on the catalyst. When a chlorine-containing compound is introduced into such a regeneration zone, it also is generally combusted or oxidized, and by-products of combustion, such as carbon dioxide, water, hydrogen chloride, and chlorine, are formed. As the chlorine-containing compound combusts, regions of intense burning can arise in the regeneration zone, either in portions of the catalyst and/or near to mechanical internals within the regeneration zone.
Two problems associated with localized regions of intense combustion of the chlorine-containing compound within the regeneration zone are catalyst deactivation and mechanical failure. As to catalyst deactivation, the combination of temperature, water vapor, and exposure time determine the useful life of the catalyst. Exposure of high surface area catalyst to high temperatures for prolonged periods of time will transform the catalyst into a more amorphous material that has a decreased surface area. Decreased surface area in turn can lower the activity of the catalyst to a level at which the catalyst is considered deactivated. This type of catalyst deactivation is permanent and can eventually render the catalyst unusable. Similarly, with respect to mechanical failure, the exposure of the internal mechanical parts of the regeneration zone to high temperatures for extended periods of time will change the physical properties of the parts and degrade or weaken their structural integrity. Consequently, the internal parts can break or crack, thereby necessitating costly repairs and downtime.
This invention is a method of introducing a halogen-containing compound that contains hydrogen or carbon into a catalyst regeneration zone. The method of this invention precombusts at least a portion of the hydrogen or carbon of the halogen-containing compound prior to using the halogen for catalyst regeneration. This invention is useful even though the catalyst regeneration zone operates at conditions that are sufficient to combust at least a portion of the hydrogen or carbon of the halogen-containing compound. By precombusting some or preferably all of the hydrogen or carbon of the halogen-containing compound in a precombustion zone, rather than in the regeneration zone, the possibility of localized regions of intense combustion of the halogen-containing compound in the regeneration zone is minimized or eliminated. Thus, this invention decreases the exposure of the catalyst to high temperatures, decreases the risk of permanent catalyst deactivation because of surface area decline, and prolongs the activity of the catalyst even after many regenerations. This invention also decreases the exposure of the internals of the regeneration zone to high temperatures, decreases the risk of weakening the internals of the regeneration tower, and prolongs the useful life of the mechanical equipment employed for regeneration.
Accordingly, in one embodiment, this invention is a method for regenerating a hydrocarbon conversion catalyst. At least a portion of the hydrogen or the carbon of a halogen-containing compound comprising hydrogen or carbon is precombusted in a precombustion zone. The hydrocarbon conversion catalyst is at least partially regenerated in the presence of the halogen in a regeneration zone at regeneration conditions comprising a regeneration temperature.
In a more specific embodiment, this invention is a hydrocarbon conversion process. A hydrocarbon feedstock is passed to a reaction zone where the feedstock is contacted with catalyst particles containing platinum. A hydrocarbon product is recovered from the reaction zone. Catalyst particles are withdrawn from the reaction zone and passed to a regeneration zone. Oxygen and perchloroethylene are passed to a precombustion zone, where at least 95% of the perchloroethylene that is passed to the precombustion zone is precombusted, thereby generating heat of the precombustion in the precombustion zone. A precombustion effluent stream comprising oxygen and molecular chlorine is withdrawn from the precombustion zone and passed to a cooling zone where the precombustion effluent stream is cooled. A cooled precombustion effluent stream comprising oxygen and molecular chlorine and having a precombustion effluent temperature of less than a regeneration temperature is withdrawn from the cooling zone. The precombustion effluent stream is passed to a regeneration zone that contains catalyst particles. In the regeneration zone, catalyst particles are contacted with the precombustion effluent stream and at least a portion of the platinum on the catalyst particles in the regeneration zone are redispersed at regeneration conditions. The regeneration conditions comprise a regeneration temperature of less than 1100xc2x0 F. Catalyst particles are withdrawn from the regeneration zone, and catalyst particles are passed to the reaction zone.
U.S. Pat. No. 3,652,231 (Greenwood et al.) describes a process and apparatus for continuous catalyst regeneration which are used in conjunction with catalytic reforming of hydrocarbons. U.S. Pat. No. 3,647,680 (Greenwood et al.) and U.S. Pat. No. 3,692,496 (Greenwood et al.) also deal with regeneration of reforming catalyst. The teachings of U.S. Pat. Nos. 3,652,231, 3,647,680, and 3,692,496 are hereby incorporated in full into this patent application.
U.S. Pat. No. 4,687,637 (Greenwood) describes a process for continuous catalyst regeneration in which a halogenation agent, such as an organic chloride, is injected into an air stream, which is then heated and introduced into a halogenation section of a regeneration tower. The teachings of U.S. Pat. No. 4,687,637 are hereby incorporated in full into this patent application.
U.S. Pat. No. 5,498,756 (Micklich et al.) describes a process and apparatus for introducing a mixture of a chlorine compound and a drying gas into a two-pass baffle that is internal to the catalyst regeneration vessel. The teachings of U.S. Pat. No. 5,498,756 are hereby incorporated in full into this patent application.
Destruction of halogenated hydrocarbons is described on pages 1052-1053 of the article by R. L. Berglund, entitled xe2x80x9cIndustrial Exhaust Control,xe2x80x9d at pages 1022-1060 of Vol. 9 of Kirk-Othmer Encyclopedia of Chemical Technology (4th Ed), published in 1994 by John Wiley and Sons. This article also describes process and catalyst considerations that are pertinent to catalytic oxidation in general, such as the performance of catalytic metals, including vanadium, chromium, manganese, iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold. In addition, this article describes the use of catalyst carriers and of catalyst supports such as spherical and cylindrical pellets, rods, ribbons, and honeycombs.
The use of platinum and palladium for the catalytic oxidation of halogenated hydrocarbons are known. Use of platinum on gamma-alumina for this purpose is described in the article by G. C. Bond et al., entitled xe2x80x9cCatalysed Destruction of Chlorinated Hydrocarbons,xe2x80x9d J. Appl. Chem. Biotechnol., 1975, 25, pages 241-248, and the article by Y. Wang et al., entitled xe2x80x9cCatalytic Oxidation of Trace Concentrations of Trichloroethylene over 1.5% Platinum on Gamma-Alumina,xe2x80x9d beginning at page 125 in Catalytic Control of Air Pollution: Mobile and Stationary Sources, edited by R. G. Silver et al. and published in American Chemical Society Symposium Series 495 in 1992. The above-mentioned article by R. L. Berglund entitled xe2x80x9cIndustrial Exhaust Control,xe2x80x9d however, points out that catalyst deactivation by halogen degradation of the catalyst carrier or the washcoat may be a problem with platinum-containing catalysts. The use of palladium oxide on gamma-alumina is described in the article by Tai-Chiang Yu et al., entitled xe2x80x9cCatalytic Oxidation of Trichloroethylene over PdO Catalyst on Gamma-Alumina,xe2x80x9d beginning at page 141 in the above-mentioned American Chemical Society Symposium Series 495. Use of oxides of platinum, palladium, or other platinum group metals on a high acidity support such as gamma-alumina, delta-alumina, theta-alumina, transitional forms of alumina, silica-alumina, and zeolites is described in U.S. Pat. No. 5,451,388 (Chen et al.). Use of a catalyst that comprises a platinum group metal, zirconium oxide, and at least one oxide selected from the group consisting of manganese oxide, cerium oxide, and cobalt oxide, and that is substantially free of vanadium is described in PCT International Publication No. WO 96/20787, which has an International Application No. PCT/US95/08060.
The use of metals other than platinum and palladium for the catalytic oxidation of halogenated hydrocarbons is also known. The article by James J. Spivey entitled xe2x80x9cComplete Catalytic Oxidation of Volatile Organics,xe2x80x9d Ind. Eng. Chem. Res., 1987, 26, 2165-2180 reviews the literature dealing with catalytic oxidation and cites uses of Cr2O3 on alumina to oxidize CH2Cl2, C2H2Cl2, and CH3Cl. Uses of vanadia alumina, of chromia alumina, and of another non-noble metal catalyst on a honeycomb support are described in the article by J. R. Kittrell et al., entitled xe2x80x9cDirect Catalytic Oxidation of Halogenated Hydrocarbons,xe2x80x9d J. Air Waste Manage. Assoc., vol. 41, no. 8, August 1991, 1129-1133. Use of copper is described in the article by Jong-Liang Lin et al., entitled xe2x80x9cThermal Decomposition of Halogenated Hydrocarbons on a Cu(111) Surface,xe2x80x9d beginning at page 153 in the previously mentioned American Chemical Society Symposium Series 495. Use of zeolite catalysts Hxe2x80x94Y, Crxe2x80x94Y, and Cexe2x80x94Y to oxidize methylene chloride in air is described in the article by S. Chatterjee et al., entitled xe2x80x9cOxidative Catalysis of Chlorinated Hydrocarbons by Metal-Loaded Acid Catalysts,xe2x80x9d Journal of Catalysis, 1991, 130, 76-85 (1991). Use of vanadium oxide, zirconium oxide, and least one oxide of manganese, cerium, or cobalt is described in U.S. Pat. No. 5,283,041 (Nguyen et al.). Use of oxides of vanadium, chromium, manganese, iron, nickel, cobalt, or copper on a high acidity support is described in previously mentioned U.S. Pat. No. 5,451,388 (Chen et al.).